1. Field of the Invention
The present invention relates to a carriage driving device for moving a carriage along a platen surface arranged in a printing apparatus such as a typewriter, a printer.
2. Description of Related Art
Conventionally, there are proposed various driving devices each of which is utilized for moving a carriage in a printing apparatus such as a typewriter or a printer. For instance, it is disclosed a carriage driving device in Japanese Patent Application, laid open No. Sho. 62-42,794 after substantive examination. In the carriage driving device, a main round guide bar having a rack at a side thereof is arranged along a platen, and both a pinion meshed with the rack and a driving motor for rotating the pinion are firmly mounted on a carriage. Further, a sub-guide bar is arranged parallel with the main guide bar so as to maintain a predetermined positional relationship of the carriage against the platen and the sub-guide bar is supported in an open recess formed in a rear part of the carriage so that the carriage can slidably move along the platen through cooperation of the sub-guide bar and the open recess.
However, according to the conventional carriage driving device mentioned above, unless the sub-guide bar is precisely arranged parallel with the main guide bar, it cannot be stably retained a positional relationship of the carriage against the platen, thereby the carriage cannot be stably moved while maintaining the predetermined positional relation with the platen. Further, in the conventional carriage driving device, the driving motor with the pinion is firmly mounted on the carriage. Therefore, in case that there exists an error in a distance with which the pinion is positioned against the main guide bar, various problems occur. For instance, if the distance between the main guide bar and the pinion is too wide, backlash occurring when the pinion meshes with the rack becomes too large. As a result, when the moving direction of the carriage is changed from the forward direction to the reverse direction, there occurs errors ill carriage movement. For example, there occurs a movement error of the carriage when the moving direction of the carriage is changed form the right direction to the left direction. And there occurs a timing error of the carriage movement. Thus, there is a problem that print quality of characters printed by the printing apparatus is deteriorated due to that pitches between the printed characters become irregular.
On the contrary, if the distance between the main guide bar and the pinion is too narrow, meshing load between the rack and the pinion becomes too large, thereby the driving motor is overloaded due to the meshing load occurring between the rack and the pinion. As a result, the carriage cannot be smoothly moved.